Pathogenicity of Fusobacterium necrophorum strains from man and animals.

Necrobacillosis occurs in man and animals. The typical forms of the disease in animals are caused by Fusobacterium necrophorum biovar A; biovar B strains are much less pathogenic. In this study the pathogenicity for mice of eight human isolates of F. necrophorum was compared with that of animal biovar A and B strains. By subcutaneous inoculation seven of the human strains differed from biovar A but resembled biovar B in (1) producing, at the most, mild local lesions that rapidly healed, and (2) showing no enhancement of infectivity when suspended in sub-lethal doses of Staphylococcus aureus broth culture. The eighth human strain (A2433) resembled biovar A but differed from biovar B in (1) producing severe lesions, and (2) showing greatly enhanced infectivity in the presence of S. aureus. Nonetheless, strain A2433 differed from biovar A, both in the nature of the lesions produced and in its failure to cause severe general signs of illness and rapidly fatal infection. By intravenous inoculation one of two biovar B strains and all except one of the eight human strains produced purulent lesions, often severe, in the liver and elsewhere, but infection was not usually associated with general signs of illness. In contrast, intravenous injection of a biovar A strain gave rise to a rapidly fatal infection, with severe lesions in the liver or elsewhere. The results suggest that the term 'necrobacillosis' as used in human and veterinary medicine refers to diseases that differ in important respects.